It’s always been said that you can’t tell a book by its cover. But sometimes book titles reveal something about authors. That’s certainly the case for two notable Democrats, Sen. Elizabeth Warren (D-Mass.) and Hillary Rodham Clinton.

Warren’s book, published this past week, is called “A Fighting Chance.” Clinton’s book, a memoir of her four years as secretary of state, is due out in June under the title “Hard Choices.” Warren’s title is aspirational, hinting at the world as it might be, a place where power would be more equitably distributed. Clinton’s title conveys a world in which the ideal and the real clash constantly and in which progress can be maddeningly slow.

Clinton is widely assumed to be running for president in 2016; Warren spent the week of her book tour saying she is not. But as two of the Democratic Party’s brightest stars, they are destined to play central roles in shaping the party’s direction after the Obama presidency ends. Whether they end up as rivals for the Democratic nomination is beside the point.

Warren has become a hero to many Democrats because she speaks forthrightly about the powerful and the powerless. She says she learned about how the world works from her research into the root causes of personal bankruptcy. She decries the mismatch between big corporations — along with their armies of lobbyists in Washington — and an economically squeezed middle class to which politicians pay lip service but do not always deliver real service.

Her deeply personal book speaks directly to the widespread feeling of so many Americans — across party lines — that the deck is stacked against them. The senator from Massachusetts shares that worldview and writes about it in terms of her own life experiences. She grew up in a struggling family in Oklahoma. Her father lost his job after having a heart attack, and her mother took a minimum-wage job to help provide for the family.

Hillary Clinton and Elizabeth Warren. (AP photos)

Her parents, Warren says, never expected her to go to college. But she did. Now she has reached rarefied levels of society, first as a Harvard Law School professor and now as a senator. Yet she continues to speak from a perspective distinct from those two elite worlds. “I am an outsider,” she said in an interview with NPR. “I’ll always be an outsider.”

She is a scourge to big banks and financial institutions, making her a beacon of the progressive wing of the Democratic Party. These Democrats have responded enthusiastically to her populist message. They want a fighter to help lead their party. They aren’t sure if the current president will ever quite fulfill their hopes, and they wonder whether a candidate Clinton would take up the cause with the passion and commitment of Warren.

Whether Warren is quite what her admirers — or detractors — believe her to be is another matter. Centrist Democrats view her call for expanding Social Security benefits rather than cutting them as fiscal malpractice. But the Economist magazine, in its current issue, questions whether she truly has policies that match her rhetoric, policies that would create a more level playing field.

Regardless, at a time of more intense focus on income inequality and on a political system in Washington that many Americans believe is unresponsive to their needs, she has captured imaginations as few others in her party have.

Clinton’s appeal is different. She could never claim to be an outsider; not with her résumé. She has long lived in a world of power, money and privilege. The Clintons’ mantra has always been to focus on the middle class, but whether she will be a rousing advocate for the populist yearnings within her party won’t really be known until she decides about 2016.

She has something else with which to create excitement, however. When she first ran for president in 2008, she symbolized the aspiration of many women — and the hope of many men — to see the ultimate glass ceiling shattered. Now, after the 18 million cracks she put in that ceiling in 2008, she is seen not just as a symbol but potentially as the vehicle for finally breaking through it.

Clinton’s forthcoming book differs from Warren’s in significant ways. It does not offer a full life story. She told much of that story in her earlier book, “Living History.” Nor is it advertised as a book about domestic or economic policy. Rather, it reportedly will lay out her accomplishments as secretary of state while offering more insight into her worldview, distinct from Obama’s.

She has always resisted being pigeonholed, though friend and foe have done plenty of it on her behalf. She is grounded in the New Democrat philosophy that carried Bill Clinton to the White House, and yet she is seen by those who have worked for her as holding more populist economic views than her husband. She will polarize the electorate, almost no matter where she draws that line.

But the title of her book, “Hard Choices,” succinctly sums up the way she has long seen her role in public service. “I approach each issue and problem from a perspective of combining my beliefs and ideals with a search for practical solutions,” she once said in an interview.

A few months ago, Clinton’s tenure at the State Department was being compared unfavorably to that of her successor, John F. Kerry. The current secretary was winning praise for tireless and risky diplomacy that had led to negotiations and the prospect of progress on three of the world’s most difficult problems: Iran’s quest for nuclear weapons, the civil war in Syria and Middle East peace.

Today, talks between Israel and the Palestinians have broken off. The negotiations over Syria have gone nowhere. Meanwhile, much work remains to bring the Iran negotiations to fruition, and Clinton has said she is skeptical about a successful outcome. The comparisons between Kerry’s record and Clinton’s look far different than they did at the beginning of this year.

I once asked a person who knew her well to sum up Clinton’s philosophy about public service. She pointed to words attributed to John Wesley, which Clinton absorbed as a young Methodist in the Chicago suburbs. On Saturday, Clinton recited the same lines during a speech to the United Methodist Women’s Assembly meeting in Louisville.

It was Wesley who said, “Do all the good you can. By all the means you can. In all the ways you can. In all the places you can. At all the times you can. To all the people you can. As long as ever you can.”

What that conveys is a kind of methodical incrementalism and a belief that, while goals may be clear, the means to achieve them are more opaque. That approach probably won’t satisfy those drawn to Warren’s more fiery populism, but it might be what a candidate Clinton actually would be selling, whatever rhetoric she might adopt for her message.

Clinton and Warren are of the same generation, born just two years apart, but they have arrived at this moment occupying different spaces within their party that reflect their real-world experiences. As their book titles suggest, each has something to offer the other.